1. Field of the Invention
This invention relates to a variable temperature stage device for an electron microscope and more particularly to such device comprising a goniometer, means detachable from the goniometer for supporting a specimen holder, means connected with the goniometer for selectively cooling the specimen holder and means for selectively cooling the specimen holder.
2. Description of the Prior Art
It is known that the main difficulty in the fabrication of a variable temperature stage device lies in the fact that the following factors have to be harmonized with each other:
firstly, the need to maintain the freedom of displacement of the goniometer on which the detachable support elements of the specimen holder are positioned and to make it possible to insert the equipment which supports the specimen to be analysed, through an entry port of the microscope chamber, and
secondly, the need to ensure that the specimen holder can be cooled and heated across a wide range of temperatures and to reduce any vibrations that might impair the resolution of the electron microscope.
In certain known variable temperature stage devices, the means for cooling the detachable supporting means includes a copper braid in contact with a container filled with a cooling liquid. The heat exchange between the cooled detachable supporting means and the specimen holder is effected through a simple metal-to-metal interface between the cold head of the goniometer and the detachable supporting means. In this case, the minimum temperature achieved is often excessively high, in the range of 100 degrees Kelvin when a cooling agent such as liquid nitrogen is in the goniometer head. In this respect, reference could be made to the embodiment described in the German Patent Application No. 2,138,567 which concerns a specimen holder inserted through a microscope port and cooled by means of metallic contact with a liquid helium container, although this type of microscope does not comprise a goniometer.
Other known variable temperature stage devices use cooling means in the form of circulation of liquid in or around a specimen holder supporting means itself, as disclosed in the German Patent Application No. 1,910,771. This arrangement does not enable the specimen to be inserted through the entry port. The heating means of these stage devices are generally provided by the Joule effect through a heating resistor which is embedded in the specimen holder.
The heating means of greater complexity may be provided by an electron stream which is directed towards the side of the specimen holder which is opposite the one supporting the specimen, as described in the German Patent Application No. 1,910,771. However, this mode of heating calls for effective means of protection against the electron stream.